U.S. patent number 6,415,736 [Application Number 09/343,481] was granted by the patent office on 2002-07-09 for gas distribution apparatus for semiconductor processing.
This patent grant is currently assigned to Lam Research Corporation. Invention is credited to Rajinder Dhindsa, Fangli Hao.
United States Patent |
6,415,736 |
Hao , et al. |
July 9, 2002 |
Gas distribution apparatus for semiconductor processing
Abstract
A gas distribution system for semiconductor processing includes
a contoured surface to achieve a desired gas distribution on the
backside of a showerhead. The system can include one or more gas
supplies opening into a plenum between a baffle plate and a
temperature-controlled support member. The baffle plate can have a
nonuniform thickness and geometry-controlled openings to achieve a
desired gas distribution. In one arrangement the baffle plate is
conical in shape with uniform diameter holes extending different
distances through the baffle plate to achieve a uniform pressure of
gas through outlets in a planar bottom surface of the baffle plate.
In another arrangement, the holes have progressively larger
diameters in a direction away from the location of the centrally
located gas supply outlet. The shape of the baffle plate and/or
configuration of the holes can be designed to achieve a desired gas
pressure distribution.
Inventors: |
Hao; Fangli (Cupertino, CA),
Dhindsa; Rajinder (San Jose, CA) |
Assignee: |
Lam Research Corporation
(Fremont, CA)
|
Family
ID: |
23346287 |
Appl.
No.: |
09/343,481 |
Filed: |
June 30, 1999 |
Current U.S.
Class: |
118/723E;
118/723ER; 156/345.34; 156/345.43; 156/345.47 |
Current CPC
Class: |
H01L
21/67017 (20130101) |
Current International
Class: |
H01L
21/00 (20060101); C23C 016/00 (); H05H
001/00 () |
Field of
Search: |
;118/715,723VE,723R,723E
;156/345 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
0452745 |
|
Oct 1991 |
|
EP |
|
02188916 |
|
Jul 1990 |
|
JP |
|
6-151336 |
|
May 1994 |
|
JP |
|
10064831 |
|
Mar 1998 |
|
JP |
|
11204444 |
|
Jul 1999 |
|
JP |
|
Other References
Notification of Transmittal of International Preliminary
Examination Report dated Sep. 6, 2001 for PCT/US00/16143,
International Filind Date Jun. 12, 2000, Priority Date Jun. 30,
1999..
|
Primary Examiner: Mills; Gregory
Assistant Examiner: Hassanzadeh; P.
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis,
LLP
Claims
What is claimed is:
1. A gas distribution system useful for semiconductor substrate
processing, comprising:
a support body;
a gas distribution chamber;
a gas supply inlet through which pressurized process gas flows into
the gas distribution chamber;
a showerhead supported by the support body such that pressurized
process gas in the gas distribution chamber applies pressure to a
backside of the showerhead and passes through openings extending
between the backside and an opposite side of the showerhead, the
showerhead being a showerhead electrode of a plasma chamber;
and
a contoured surface in the gas distribution chamber, the contoured
surface being effective to provide a desired gas pressure
distribution at the backside of the showerhead electrode, and
wherein the contoured surface comprises a nonplanar upper and/or
lower surface of a baffle plate having openings therethrough and
the gas distribution chamber comprises an upper plenum above the
baffle plate and a lower plenum below the baffle plate.
2. The gas distribution system of claim 1, wherein the baffle plate
has uniformly sized openings extending between the upper and lower
surfaces, the openings having shorter lengths in a central portion
of the baffle plate and longer lengths in an outer portion of the
baffle plate.
3. The gas distribution system of claim 1, wherein the baffle plate
is integral with the support body, the upper plenum is enclosed by
an upper sidewall of the support body and a cover plate which seals
against the upper sidewall, and the lower plenum is enclosed by a
lower sidewall of the support body and the showerhead which seals
against the lower sidewall.
4. The gas distribution system of claim 1, wherein the openings
become progressively larger at locations away from the gas supply
inlet.
5. The gas distribution system of claim 1, wherein the baffle plate
has a conical shape, the openings have the same diameters and the
openings have different lengths through the baffle plate.
6. The gas distribution system of claim 1, wherein at least some of
the outlets are tapered.
7. A gas distribution system useful for semiconductor substrate
processing, comprising:
a support body;
a gas distribution chamber;
a gas supply inlet through which pressurized process gas flows into
the gas distribution chamber,
a showerhead supported by the support body such that pressurized
process gas in the gas distribution chamber applies pressure to a
backside of the showerhead and passes through openings extending
between the backside and an opposite side of the showerhead, the
showerhead being a showerhead electrode of a plasma chamber;
and
a contoured surface in the gas distribution chamber, the contoured
surface being effective to provide a desired gas pressure
distribution at the backside of the showerhead electrode wherein
the contoured surface is a nonplanar lower surface of the support
body and the gas distribution chamber comprises an open space
between the contoured surface and the backside of the showerhead
wherein the showerhead is spaced closer to the contoured surface in
the vicinity of the gas supply inlet and further from the contoured
surface at locations away from the gas supply inlet.
8. The gas distribution system of claim 7, wherein the gas inlet
supplies process gas through an annular channel which opens into an
outer region of the open space and the showerhead is spaced closer
to the contoured surface in the outer region and further from the
contoured surface in a central region of the open space.
9. A gas distribution system useful for semiconductor substrate
processing, comprising:
a support body;
a gas distribution chamber;
a gas supply inlet through which pressurized process gas flows into
the gas distribution chamber;
a showerhead supported by the support body such that pressurized
process gas in the gas distribution chamber applies pressure to a
backside of the showerhead and passes through openings extending
between the backside and an opposite side of the showerhead;
and
a contoured surface in the gas distribution chamber, the contoured
surface being effective to provide a desired gas pressure
distribution at the backside of the showerhead, the contoured
surface comprising a nonplanar upper and/or lower surface of a
baffle plate having openings therethrough and the gas distribution
chamber comprising an upper plenum above the baffle plate and a
lower plenum below the baffle plate, the gas inlet supplying the
process gas through a central opening in a planar surface facing
the baffle plate, the baffle plate having a thickness which is
larger in a central portion of the baffle plate and smaller at an
outer portion of the baffle plate.
10. A gas distribution system useful for semiconductor substrate
processing, comprising:
a support body;
a gas distribution chamber;
a gas supply inlet through which pressurized process gas flows into
the gas distribution chamber;
a showerhead supported by the support body such that pressurized
process gas in the gas distribution chamber applies pressure to a
backside of the showerhead and passes through openings extending
between the backside and an opposite side of the showerhead;
and
a contoured surface in the gas distribution chamber, the contoured
surface being effective to provide a desired gas pressure
distribution at the backside of the showerhead, the contoured
surface comprising a nonplanar upper and/or lower surface of a
baffle plate having openings therethrough and the gas distribution
chamber comprising an upper plenum above the baffle plate and a
lower plenum below the baffle plate, the gas inlet supplying the
process gas through an inlet which opens into an outer region of
the upper plenum, the baffle plate having a thickness which is
smaller in a central portion of the baffle plate and larger at an
outer portion of the baffle plate.
11. A gas distribution system useful for semiconductor substrate
processing, comprising:
a support body;
a gas distribution chamber;
a gas supply inlet through which pressurized process gas flows into
the gas distribution chamber;
a showerhead supported by the support body such that pressurized
process gas in the gas distribution chamber applies pressure to a
backside of the showerhead and passes through openings extending
between the backside and an opposite side of the showerhead;
and
a contoured surface in the gas distribution chamber, the contoured
surface being effective to provide a desired gas pressure
distribution at the backside of the showerhead, the contoured
surface comprising a nonplanar upper and/or lower surface of a
baffle plate having openings therethrough and the gas distribution
chamber comprising an upper plenum above the baffle plate and a
lower plenum below the baffle plate, the baffle plate having
uniformly sized openings extending between the upper and lower
surfaces, the openings having longer lengths in a central portion
of the baffle plate and shorter lengths in an outer portion of the
baffle plate.
12. A gas distribution system useful for semiconductor substrate
processing, comprising:
a support body;
a gas distribution chamber;
a gas supply inlet through which pressurized process gas flows into
the gas distribution chamber;
a showerhead supported by the support body such that pressurized
process gas in the gas distribution chamber applies pressure to a
backside of the showerhead and passes through openings extending
between the backside and an opposite side of the showerhead;
and
a contoured surface in the gas distribution chamber, the contoured
surface being effective to provide a desired gas pressure
distribution at the backside of the showerhead, the contoured
surface being a nonplanar lower surface of the support body and the
gas distribution chamber comprising an open space between the
contoured surface and the backside of the showerhead, the gas inlet
supplying the process gas through a central opening in the lower
surface of the support body and the open space being smaller in a
central region thereof and larger in an outer region thereof.
13. A gas distribution system useful for semiconductor substrate
processing, comprising:
a support body;
a gas distribution chamber;
a gas supply inlet through which pressurized process gas flows into
the gas distribution chamber;
a showerhead supported by the support body such that pressurized
process gas in the gas distribution chamber applies pressure to a
backside of the showerhead and passes through openings extending
between the backside and an opposite side of the showerhead;
and
a contoured surface in the gas distribution chamber, the contoured
surface being effective to provide a desired gas pressure
distribution at the backside of the showerhead, the contoured
surface comprising a nonplanar upper and/or lower surface of a
baffle plate having openings therethrough and the gas distribution
chamber comprising an upper plenum above the baffle plate and a
lower plenum below the baffle plate, the support body including at
least one coolant channel in which coolant can be circulated.
14. A gas distribution system useful for semiconductor substrate
processing, comprising:
a support body;
a gas distribution chamber;
a gas supply inlet through which pressurized process gas flows into
the gas distribution chamber;
a showerhead supported by the support body such that pressurized
process gas in the gas distribution chamber applies pressure to a
backside of the showerhead and passes through openings extending
between backside and an opposite side of the showerhead; and
a contoured surface in the gas distribution chamber, the contoured
surface being effective to provide a desired gas pressure
distribution at the backside of the showerhead, the contoured
surface comprising a nonplanar upper and/or lower surface of a
baffle plate having openings therethrough and the gas distribution
chamber comprising an upper plenum above the baffle plate and a
lower plenum below the baffle plate, the support body including a
second gas supply inlet which supplies process gas that passes
through the baffle plate.
15. A gas distribution system useful for semiconductor substrate
processing, comprising:
a support body;
a gas distribution chamber;
a gas supply inlet through which pressurized process gas flows into
the gas distribution chamber;
a showerhead supported by the support body such that pressurized
process gas in the gas distribution chamber applies pressure to a
backside of the showerhead and passes through openings extending
between the backside and an opposite side of the showerhead;
and
a contoured surface in the gas distribution chamber, the contoured
surface being effective to provide a desired gas pressure
distribution at the backside of the showerhead, the contoured
surface comprising a nonplanar upper and/or lower surface of a
baffle plate having openings therethrough and the gas distribution
chamber comprising an upper plenum above the baffle plate and a
lower plenum below the baffle plate, the openings having the same
diameters and the openings having progressively shorter lengths at
locations away from the gas supply inlet.
16. A gas distribution system useful for semiconductor substrate
processing, comprising:
a support body;
a gas distribution chamber;
a gas supply inlet through which pressurized process gas flows into
the gas distribution chamber;
a showerhead supported by the support body such that pressurized
process gas in the gas distribution chamber applies pressure to a
backside of the showerhead and passes through openings extending
between the backside and an opposite side of the showerhead;
and
a contoured surface in the gas distribution chamber, the contoured
surface being effective to provide a desired gas pressure
distribution at the backside of the showerhead, the contoured
surface comprising a nonplanar upper and/or lower surface of a
baffle plate having openings therethrough and the gas distribution
chamber comprising an upper plenum above the baffle plate and a
lower plenum below the baffle plate, the openings at a peripheral
portion of the baffle plate having larger diameters than the
openings proximate a central region of the baffle plate.
17. A gas distribution system useful for semiconductor substrate
processing, comprising:
a support body;
a gas distribution chamber;
a gas supply inlet through which pressurized process gas flows into
the gas distribution chamber;
a showerhead supported by the support body such that pressurized
process gas in the gas distribution chamber applies pressure to a
backside of the showerhead and passes through openings extending
between the backside and an opposite side of the showerhead;
and
a contoured surface in the gas distribution chamber, the contoured
surface being effective to provide a desired gas pressure
distribution at the backside of the showerhead, the contoured
surface comprising a nonplanar upper and/or lower surface of a
baffle plate having openings therethrough and the gas distribution
chamber comprising an upper plenum above the baffle plate and a
lower plenum below the baffle plate, at least some of the openings
having diameters which change along the length of the openings.
Description
FIELD OF THE INVENTION
The present invention relates to reaction chambers used for
processing semiconductor substrates, such as integrated circuit
wafers, and specifically to improvements in the gas distribution
system used in these reaction chambers.
BACKGROUND OF THE INVENTION
Semiconductor processing includes deposition processes such as
chemical vapor deposition (CVD) of metal, dielectric and
semiconducting materials, etching of such layers, ashing of
photoresist masking layers, etc. In the case of etching, plasma
etching is conventionally used to etch metal, dielectric and
semiconducting materials. A parallel plate plasma reactor typically
includes a gas chamber including one or more baffles, a showerhead
electrode through which etching gas passes, a pedestal supporting
the silicon wafer on a bottom electrode, an RF power source, and a
gas injection source for supplying gas to the gas chamber. Gas is
ionized by the electrode to form plasma. The plasma etches the
wafer supported below the showerhead electrode.
Showerhead electrodes for plasma processing of semiconductor
substrates are disclosed in commonly assigned U.S. Pat. Nos.
5,074,456; 5,472,565; 5,534,751; and 5,569,356. Other showerhead
electrode gas distribution systems are disclosed in U.S. Pat. Nos.
4,209,357; 4,263,088; 4,270,999; 4,297,162; 4,534,816; 4,579,618;
4,590,042; 4,593,540; 4,612,077; 4,780,169; 4,792,378; 4,820,371;
4,854,263; 5,006,220; 5,134,965; 5,494,713; 5,529,657; 5,593,540;
5,595,627; 5,614,055; 5,716,485; 5,746,875 and 5,888,907.
During the plasma etching process, plasma is formed above the
masked surface of the wafer by adding large amounts of energy to a
gas at relatively low pressure, ionizing the gas to form plasma. By
adjusting the electrical potential of the wafer, charged species in
the plasma can be directed to impinge perpendicularly upon the
wafer, so that materials in unmasked regions of the wafer are
removed.
It is desirable to evenly distribute the plasma over the surface of
the wafer in order to obtain uniform etching rates over the entire
surface of the wafer. Current gas distribution chamber designs
include multiple baffles which are optimized to uniformly
distribute etching gas to achieve the desired etching effect at the
wafer. Conventional gas distribution designs include baffles having
hundreds of openings or complex, difficult to manufacture
geometries to ensure even distribution of etching gas to the
backside of the showerhead electrode. Some attempts have been made
to control gas flow by using a shaped electrode. However,
manufacturing very pure silicon electrodes having complicated
geometries is difficult and expensive. When etching large,
twelve-inch (300 mm) wafers, controlling the process gas to create
a uniform pressure distribution across the showerhead is even more
difficult. The number of openings and baffles must be increased
significantly to maintain uniform distribution of the etching gas.
As the number of openings in the baffles increase and the number of
baffles increase, the complexity and cost to manufacture such a gas
distribution apparatus increase greatly.
U.S. Pat. No. 5,736,457 describes single and dual "damascene"
metallization processes. In the "single damascene" approach, vias
and conductors are formed in separate steps wherein a metallization
pattern for either conductors or vias is etched into a dielectric
layer, a metal layer is filled into the etched grooves or via holes
in the dielectric layer, and the excess metal is removed by
chemical mechanical planarization (CMP) or by an etch back process.
In the "dual damascene" approach, the metallization patterns for
the vias and conductors are etched in a dielectric layer and the
etched grooves and via openings are filled with metal in a single
metal filling and excess metal removal process.
From the foregoing it can be seen that as the size of semiconductor
substrates increases, the ability to achieve uniform distribution
of process gas above the substrates becomes more difficult.
Accordingly, there is a need in the art for improvements in gas
distribution systems. Further, to the extent that components of gas
distribution systems are regularly replaced, it would be desirable
if such components could be designed in a manner which facilitates
economical manufacture thereof.
SUMMARY OF THE INVENTION
The present invention provides a gas distribution system which
includes a contoured surface in a gas distribution chamber to
achieve desired gas distribution delivered through a showerhead.
Thus, the geometry of the contoured surface can be selected to
optimize gas flow between the showerhead and the semiconductor
substrate being processed.
The gas distribution system in accordance with the invention
preferably includes a support body, a gas distribution chamber, a
gas supply inlet, a showerhead and the contoured surface. The gas
supply inlet supplies pressurized process gas into the gas
distribution chamber and the showerhead is supported by the support
body such that pressurized process gas in the gas distribution
chamber applies pressure to a backside of the showerhead and passes
through openings extending between the backside and an opposite
side of the showerhead. The contoured surface is in the gas
distribution chamber and is effective to provide a desired gas
pressure distribution at the backside of the showerhead.
The contoured surface can be located on the support body or on a
baffle plate located in the gas distribution chamber. For instance,
the contoured surface can comprise a nonplanar upper and/or lower
surface of the baffle plate or on a lower surface of the support
body. The gas distribution chamber can comprise upper and/or lower
plenums on opposite sides of the baffle plate or an open space
between the contoured surface and the backside of the showerhead.
The support body can include at least one coolant channel in which
coolant can be circulated.
The gas inlet can open into various portions of the gas
distribution chamber. For instance, the gas inlet can supply the
process gas through a central opening in a planar surface of the
support body facing the baffle plate in which case the baffle plate
has a thickness which is larger in a central portion of the baffle
plate and smaller at an outer portion of the baffle plate.
Alternatively, the gas inlet can supply the process gas through an
annular channel which opens into an outer region of the upper
plenum in which case the baffle plate has a thickness which is
smaller in a central portion thereof and larger at an outer portion
thereof. The baffle plate can include uniformly sized openings
extending between the upper and lower surfaces thereof, the
openings having longer lengths either in the central portion of the
baffle plate or in the outer portion of the baffle plate.
In the case where the contoured surface is a lower surface of the
support body, the gas inlet can supply the process gas through a
central opening in the lower surface and the open space can be
smaller in a central region thereof and larger in an outer region
thereof. Alternatively, the gas inlet can supply the process gas
through an inlet which opens into an outer region of the open space
in which case the showerhead can be spaced further from the
contoured surface in the center region and closer to the contoured
surface in the outer region.
The contoured surface can be an upper and/or lower nonplanar
surface of a baffle section which is integral with the support body
in which case the gas distribution chamber comprises an upper
plenum above the baffle section and a lower plenum below the baffle
section. In such a case, the upper plenum can be enclosed by an
upper sidewall of the support body and a cover plate (which
optionally can include one or more coolant channels) which seals
against the upper sidewall and the lower plenum can be enclosed by
a lower sidewall of the support body and the showerhead which seals
against the lower sidewall.
BRIEF DESCRIPTION OF THE DRAWINGS
The objects and advantages of the invention will be understood by
reading the following detailed description in conjunction with the
drawings in which:
FIG. 1 is a sectional view of a gas distribution chamber according
to the present invention;
FIG. 2 is an exploded perspective sectional view of a third
embodiment of a gas distribution system according to the
invention;
FIGS. 3A-E are sectional views of various contoured surface
arrangements in accordance with the invention;
FIG. 4 is a sectional view of a baffle plate according to the third
embodiment of the invention; and
FIGS. 5A-B show an etching process which can be carried out with
the gas distribution system of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
For a better understanding of the invention, the following detailed
description refers to the accompanying drawings, wherein preferred
exemplary embodiments of the present invention are illustrated and
described. In addition, the reference numbers used to identify key
elements of the invention in the drawings are consistent
throughout.
According to the present invention, process gas can be uniformly
distributed from one or more gas supplies to a substrate positioned
underneath a showerhead. The showerhead can be used in any type of
semiconductor processing apparatus wherein it is desired to
distribute process gas over a semiconductor substrate. Such
apparatus includes CVD systems, ashers, capacitive coupled plasma
reactors, inductive coupled plasma reactors, ECR reactors, and the
like.
A gas distribution system for a parallel plate plasma reactor is
shown in FIG. 1 wherein a support plate 20 and a showerhead 22 are
secured together to define a sealed gas distribution chamber 24. A
baffle assembly 26, including one or more baffle plates, is located
between the support plate 20 and the showerhead 22. According to
the present invention, the geometry and arrangement of the baffle
assembly 26 is configured to uniformly distribute gas to a backside
28 of the showerhead 22. In semiconductor wafer processes such as
chemical vapor deposition or dry-etch plasma processes, the
controlled distribution of process gas across the substrate is
desirable in order to increase the consistency and yield of these
processes.
According to the invention, a contoured surface is used to provide
a desired gas pressure distribution on the backside of a
showerhead. The gas distribution system preferably includes a
support body, a gas distribution chamber, a gas supply inlet, a
showerhead and the contoured surface. The gas supply inlet supplies
pressurized process gas into the gas distribution chamber and the
showerhead is supported by the support body such that pressurized
process gas in the gas distribution chamber applies pressure to a
backside of the showerhead and passes through openings extending
between the backside and an opposite side of the showerhead.
The contoured surface can be located on the support body or on a
baffle plate located in the gas distribution chamber. For instance,
the contoured surface can comprise a nonplanar upper and/or lower
surface of the baffle plate or on a lower surface of the support
body. The gas distribution chamber can comprise upper and/or lower
plenums on opposite sides of the baffle plate or an open space
between the contoured surface and the backside of the showerhead.
The support body can include at least one coolant channel in which
coolant can be circulated.
The gas inlet can open into various portions of the gas
distribution chamber. For instance, the gas inlet can supply the
process gas through a central opening in a planar surface of the
support body facing the baffle plate in which case the baffle plate
has a thickness which is larger in a central portion of the baffle
plate and smaller at an outer portion of the baffle plate.
Alternatively, the gas inlet can supply the process gas through an
inlet which opens into an outer region of the upper plenum in which
case the baffle plate has a thickness which is smaller in a central
portion thereof and larger at an outer portion thereof. The baffle
plate can include uniformly sized openings extending between the
upper and lower surfaces thereof, the openings having longer
lengths either in the central portion of the baffle plate or in the
outer portion of the baffle plate.
In the case where the contoured surface is a lower surface of the
support body, the gas inlet can supply the process gas through a
central opening in the lower surface and the open space can be
smaller in a central region thereof and larger in an outer region
thereof. Alternatively, the gas inlet can supply the process gas
through an inlet such as an annular channel which opens into an
outer region of the open space in which case the showerhead can be
spaced closer to the contoured surface in the outer region and
further from the contoured surface in the central region. Also, an
inlet could be provided on only one side of the open space in which
case the contoured surface would be shaped to achieve the desired
gas pressure distribution.
The contoured surface can be an upper and/or lower nonplanar
surface of a baffle section which is integral with the support body
in which case the gas distribution chamber comprises an upper
plenum above the baffle section and a lower plenum below the baffle
section. In such a case, the upper plenum can be enclosed by an
upper sidewall of the support body and a cover plate (which
optionally can include one or more coolant channels) which seals
against the upper sidewall and the lower plenum can be enclosed by
a lower sidewall of the support body and the showerhead which seals
against the lower sidewall.
The contoured surface can be provided on a baffle plate of
non-uniform thickness and the baffle plate can include geometry
controlled openings wherein lengths and/or sizes of the openings
are varied to achieve the desired gas distribution. One embodiment
of the contoured baffle plate is shown in FIG. 2 wherein a baffle
plate 92 includes a contoured top surface 94. The baffle plate 92
is secured within a gas distribution chamber 24 defined by the
support plate 20 and the showerhead 22. The baffle plate 92
includes a peripheral wall 96 that contacts the showerhead 22 and
support plate 20. Alternatively, the baffle plate 92 may be formed
integral with support plate 20 by providing a recess in the upper
surface of the support plate and sealing the recess with a cover
plate. In the case where gas pressure is highest above the center
of the baffle plate, uniform gas pressure below the baffle plate
can be achieved by designing the contoured top surface 94 to slope
continuously from a central high portion 98 towards the periphery
of the gas distribution chamber 24. Gas passes through openings 100
which are perpendicular to a planar bottom surface 95 of the baffle
plate 92. If desired, however, some or all of the openings 100 can
be non-perpendicular to the bottom surface.
In the arrangement shown in FIG. 2, process gas is delivered
through a generally centrally located gas supply 102. However, gas
may be supplied through a non-centrally located gas supply and/or
multiple gas supplies. In the plenum between support plate 20 and
the upper surface 94 of the baffle plate 92, process gas pressure
is greatest nearest the centrally located gas supply inlet 102 and
decreases towards the periphery of the baffle plate 92. Pressure
losses due to friction occur as the gas passes through the openings
100 in the baffle plate 92. For openings having a circular
cross-section, such a pressure drop can be represented by the
formula C.varies.D.sup.3 /L wherein C is the gas flow conductance,
D is the hole diameter and L is the length of the holes. Generally,
for equal sized openings, an opening having a longer length creates
a greater pressure loss due to friction than a shorter opening.
Likewise, a change in diameter of an opening causes a more dramatic
effect on the change in frictional pressure losses than a
proportional change in length of the opening since the flow rate of
gas is proportional to the diameter of the opening cubed and
directly inversely proportional to the length of the opening.
The slope of the top surface 94 of the baffle plate 92 can be
designed to achieve desired change in length of openings 100 across
the baffle plate 92. In the embodiment shown, the longest opening
begins at the high central portion 98 of the baffle plate 92 where
the inlet gas pressure is greatest. Due to the sloping surface, the
farther an opening is from the high central portion 98 of the
baffle plate 92 the shorter its length. With this geometry
controlled baffle plate design, it is possible to select the slope
of the contoured top surface 94 of the baffle plate 92 and the
position of the openings 100 through the baffle plate 92, such that
a substantially uniform pressure distribution can be created as gas
exits the baffle plate 92 and contacts a backside 28 of the
showerhead 22. If a controlled nonuniform pressure distribution is
desired, the openings 100 and contour of baffle plate 92 may be
selected to create the desired pressure distribution.
The diameter of the openings 100 can be the same across the baffle
plate or the diameters can be varied, e.g., large diameter openings
104 can be positioned near the periphery of the baffle plate 92 to
provide small frictional pressure losses to relatively low-pressure
gas flowing through the openings in the periphery of the baffle
plate 92. In a modified geometry controlled baffle plate, the
baffle plate can have any desired shape and/or nonuniform hole
sizes and/or angle of the holes can be varied to achieve a desired
pressure distribution. For instance, if uniform pressure is desired
across the showerhead, in a centrally fed gas distribution system
the holes can have larger diameters at the periphery of the baffle
plate and smaller diameters in the central portion. Conversely, in
a gas distribution system wherein the process gas is fed to the
periphery of the plenum, the holes can be larger in the middle of
the baffle plate.
Various embodiments of the contoured surface 94 are shown in FIGS.
3A-E. In FIG. 3A, the contoured surface 94 is an upper surface of a
baffle plate 92, the gas inlet 102 supplies process gas to a
central portion of the gas distribution chamber 24 and the baffle
plate 92 is thicker in the middle and thinner at the outer portion
thereof. Thus, in the region where the gas pressure is highest
(i.e., where the gas inlet 102 opens into the chamber 24), the
openings 100 through the baffle plate are longer and thus serve to
lower the gas pressure of the process gas passing therethrough as
it enters the lower plenum 24a between the baffle plate 92 and the
showerhead 22. As shown in FIG. 3A, the support body 20 can include
one or more coolant channels 21.
FIG. 3B shows an arrangement wherein the baffle plate 92 is
integral with the support body 20. In this case, the contoured
surface 94 is an upper surface of the support body 20 and the gas
distribution chamber 24 includes an upper plenum between the baffle
section 92 and a cover plate 20a and a lower plenum 24a between the
baffle section 92 and the showerhead 22. The plenums 24 and 24a are
further enclosed by sidewalls 20b, 20c of the support body 20.
FIG. 3C shows an arrangement wherein the contoured surface 94 is a
lower surface of a baffle plate 92. In this arrangement, the gas
inlet 102 opens into a central portion of an upper plenum 24 and
the baffle plate 92 is thicker in the middle thereof and thinner at
the outer portion thereof. As a result, the openings 100 are longer
in the central portion of the baffle plate 92 and thus are
effective in reducing the gas pressure as the gas passes through
the central portion of the baffle plate 92. Thus, like the
arrangement wherein the contoured surface 94 is an upper surface of
the baffle plate 92, the arrangement shown in FIG. 3C is effective
in obtaining a uniform distribution of gas pressure on the backside
of the showerhead 22.
FIG. 3D shows an arrangement wherein the gas inlet 102 opens into
an annular channel extending around an upper plenum 24 whereby the
process gas enters an outer region of the upper plenum 24. As a
result, the gas pressure is highest in the vicinity of the annular
channel 102a and the gas pressure becomes lower towards the central
region of the plenum 24. The contoured surface 94 is an upper
surface of a baffle plate 92, the baffle plate 92 being thicker at
an outer portion thereof and thinner in the central portion
thereof. Thus, the openings 100 are longer in the outer portion and
shorter in the central portion of the baffle plate. As a result,
the gas pressure of the process gas passing through the openings in
the outer portion of the baffle plate is reduced by the time the
process gas enters the lower plenum 24a to provide a more uniform
distribution of gas pressure on the backside of the showerhead
22.
FIG. 3E shows an arrangement wherein the contoured surface 94 is a
lower surface of the support body 20. In the arrangement shown, the
gas inlet 102 opens into an annular channel at the outer portion of
the gas distribution chamber 24. As such, the pressure drop of the
gas is reduced in the central region of the chamber 24. Because the
contoured surface 94 slopes towards the showerhead 22 and thus
decreases the distance between the contoured surface 94 and the
backside of the showerhead 22 in a direction towards the outer
portion of the showerhead 22, the gas pressure at the backside of
the showerhead 22 can be made more uniform. However, if the gas
inlet 102 opens into the center of the chamber 24, the contoured
surface 94 would be reversed such that the distance between the
contoured surface 94 and the backside of the showerhead is greatest
at the outer portion of the showerhead and smallest in the central
portion of the showerhead.
Each opening through the sloping body has an outlet 106 that opens
above the showerhead 22. As shown in FIG. 4, the outlets 106 can be
stepped or tapered (e.g., the hole diameter can be largest at the
surface 95) at any desired location on the baffle plate so as to
act as diffusers to control the pressure of gas exiting the baffle
plate 92. The tapered outlets 106 effect a pressure drop in the gas
exiting the openings 100 whereas stepped (i.e., abrupt change in
diameter) outlets 107 can effect a much greater pressure drop as
gas exits the opening. By including a baffle plate having
nonuniform thickness and geometry controlled openings, the present
invention achieves the desired gas distribution uniformity even
when processing large twelve-inch wafers.
FIGS. 5A-B show schematics of how a dual-damascene structure can be
etched in a single step in accordance with the invention. FIG. 5A
shows a pre-etch condition wherein an opening 500 corresponding to
a trench is provided in a photoresist masking layer 520 which
overlies a stack of a first dielectric layer 540 such as silicon
oxide, a first stop layer 560 such as silicon nitride, a second
dielectric layer 580 such as silicon oxide, a second stop layer 600
such as silicon nitride, and a substrate 620 such as a silicon
wafer. In order to obtain etching of vias through the first stop
layer 560 in a single etching step, first stop layer 560 includes
an opening 640. FIG. 5B shows the structure after etching wherein
the opening 500 extends through the dielectric layer 540 to the
first stop layer 560 and the opening 640 extends through the second
dielectric 580 to the second stop layer 600. Such an arrangement
can be referred to as a "self-aligned dual-damascene"
structure.
During the etch process, process gas conditions supplied by the
first and second gas supplies in the first and second embodiments
can be changed relative to each other, e.g., during etching of the
trench 500 a mixture of Ar, oxygen and fluorocarbons (e.g.,
CHF.sub.3 and C.sub.4 F.sub.8) can be supplied and during etching
of the vias 640 the flow of the oxygen to the central region of the
wafer can be decreased. Thus, according to the invention the flow
of gases to the center and edge of the wafer can be adjusted to
compensate for edge fast etching and center fast etching conditions
in the plasma chamber. For example, in a conventional plasma
etcher, edge fast etch conditions can occur until the photoresist
is eroded after which center fast etch conditions can occur. With
the gas distribution apparatus according to the invention, more
oxygen can be supplied in the center when the wafer has a
photoresist layer whereas when the photoresist layer is eroded
away, the flow of oxygen to the center can be reduced. As a result,
more uniform etching can be achieved by compensating for the
edge-fast and center-fast etch conditions.
The process of the invention is applicable to various plasma
processes including plasma etching of various dielectric layers
such as doped silicon oxide such as fluorinated silicon oxide
(FSG), undoped silicon oxide such as silicon dioxide, spin-on-glass
(SOG), silicate glasses such as boron phosphate silicate glass
(BPSG) and phosphate silicate glass (PSG), doped or undoped
thermally grown silicon oxide, doped or undoped TEOS deposited
silicon oxide, etc. The dielectric dopants include boron,
phosphorus and/or arsenic. The dielectric can overlie a conductive
or semiconductive layer such as polycrystalline silicon, metals
such as aluminum, copper, titanium, tungsten, molybdenum or alloys
thereof, nitrides such as titanium nitride, metal silicides such as
titanium silicide, cobalt silicide, tungsten silicide, molybdenum
silicide, etc.
The plasma can be a high density plasma produced in various types
of plasma reactors. Such plasma reactors typically have high energy
sources which use RF energy, microwave energy, magnetic fields,
etc. to produce the high density plasma. For instance, the high
density plasma could be produced in a transformer coupled plasma
(TCP.TM.) which is also called inductively coupled plasma reactor,
an electron-cyclotron resonance (ECR) plasma reactor, a helicon
plasma reactor, or the like. An example of a high flow plasma
reactor which can provide a high density plasma is disclosed in
commonly owned U.S. Pat. No. 5,820,723, the disclosure of which is
hereby incorporated by reference.
The present invention has been described with reference to
preferred embodiments. However, it will be readily apparent to
those skilled in the art that it is possible to embody the
invention in specific forms other than as described above without
departing from the spirit of the invention. The preferred
embodiment is illustrative and should not be considered restrictive
in any way. The scope of the invention is given by the appended
claims, rather than the preceding description, and all variations
and equivalents which fall within the range of the claims are
intended to be embraced therein.
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